KR100276699B1 - Power control method for the CDMA system - Google Patents

Abstract

The present invention relates to a power control method for a code division multiple access (CDMA) system, and more particularly to a power control method for determining the power of a mobile terminal received at each base station. Since the code division multiple access system performs the service using the same frequency, the capacity of the system is determined by the amount of interference received by the corresponding base station. The interference at this time is defined as the power of another mobile terminal received at the base station. Therefore, determining the reception power of the base station that minimizes the power applied to other mobile terminals while maintaining the appropriate call quality of the mobile terminal is a very important factor in determining the capacity of the code division multiple access system. In order to calculate the optimal reception power of one mobile terminal in a specific base station of a code division multiple access system, the actual traffic load of traffic in a specific base station and two adjacent cells (18 cells) surrounding the specific base station It is a method of determining the reception power of an optimal mobile terminal in a specific base station and a neighboring base station in consideration of the state. By this method, the number of mobile terminals that can be accommodated in each base station is increased by about 20% or more than the number of mobile terminals that can be accommodated by conventional power control.

Description

Power control method for code division multiple access system {Power control method for the CDMA system}

The present invention relates to a power control method for a code division multiple access (CDMA) system, and more particularly to a power control method for determining the received power of one mobile terminal at each base station.

In general, since code division multiple access systems have their capacity determined by interference, suppressing more interference than necessary from the outside is an important factor in maintaining desired call quality. In the conventional code division multiple access system, the open loop power control is closed so that the amount of power received from the mobile terminal in the cell is received at the same level regardless of the current position of the mobile terminal in order to minimize the interference from the outside. Power control techniques such as loop power control and outer loop power control are used to control the transmit power of mobile terminals.

Therefore, in order to maintain the call quality of the mobile terminal at an appropriate level (Bit Error Rate <10 ^-3 ), the ratio of bit energy to noise density at the corresponding base station must be greater than or equal to five. However, since the power received from other mobile terminals in the cell and the mobile terminals in the adjacent cell acts as interference in the mobile terminal, the power received from these mobile terminals to the base station while maintaining proper call quality is minimized as much as possible. Should be maintained.

Accordingly, the present invention provides a power control method for a code division multiple access (CDMA) system for obtaining an optimal power value received by a mobile station from a mobile station under actual traffic conditions imposed on the base station and a neighboring base station. There is a purpose.

According to an aspect of the present invention, a control station notified of a new call request determines a plurality of optimal reception powers based on a linear programming method using the base station as a central cell, and among the determined plurality of optimal reception powers. Selecting an optimal reception power to determine an optimal reception power of a corresponding base station; selecting one base station among a plurality of neighboring base stations in order, determining the center cell, and then performing a linear programming method around the center cell. Obtaining an optimal reception power and determining the first optimal reception power as the optimal reception power of the corresponding center cell; and equalizing the power of the mobile terminal reaching the base station based on the optimal reception power of the base stations obtained above. Including the step of performing power control to maintain And that is characterized.

1 is a flow chart for determining the reception power of a base station that requested a call and 18 neighboring base stations when a new call request is received from a new mobile terminal according to the present invention.

In the multi-cell code division multiple access environment, the ratio of bit energy to noise density (E _b / N ₀ ) at the base station i of a specific mobile terminal is expressed by Equation 1 below.

In Equation 1, N _i is the number of mobile terminals in the i cell, W is the spreading bandwidth, R is the transmission speed, P _i is the reception power of the base station i, η ₀ is the background noise, and f _ij is the mobile terminal in the j cell. Denotes the ratio of interference to the i cell.

Equation 1 should be 5 (7dB) to satisfy 99% or more of the performance required for the reverse link of one cell (Bit Error Rate <10 ⁻³ ). In other words, if you write Equation 1 again, Equation 2 below.

Γ = 5 in the above equation. This value is the upper limit for the modem on the reverse link to operate with adequate performance.

In order to determine the optimal power of a specific cell, when the number of mobile terminals accommodated in a neighbor cell of two stages as a center cell and N ₁ , N ₂ , N ₃ , and N ₁₉ , respectively, the corresponding mobile terminal While guaranteeing the voice quality of the power, the power received by a particular base station and 18 adjacent base stations can be obtained using Equation 3 below.

로 결정된다. 즉, 하나의 [수학식 3]을 선형계획법에 의해 풀면 19개의 수신전력을 구할 수 있는데 이중 첫번째 수신전력이 해당 셀의 최적의 수신 전력이 된다. 그러나 특정 기지국의 시스템 용량은 해당 기지국의 수신 전력과 인접 기지국으로부터 간섭되는 전력에 의해서 결정되므로 인접 기지국으로 부터의 간섭의 양을 최소화하기 위해서 해당 셀의 수신 전력 뿐만 아니라 인접 기지국의 수신전력을 결정할 필요가 있다. 따라서, 18개의 인접 셀의 최적의 수신전력을 구하기 위해서는 다음과 같은 절차를 사용한다. 즉, 18개의 인접 기지국 중의 하나를 중앙 셀로 지정한 후 그 셀을 중심으로 하여 중심 셀과 18 개의 인접 셀의 트래픽을 고려한 [수학식 3]을 다시 정의한 후 선형계획법에 의거하여 풀면 해당 중심 셀의 최적의 전력치를 구할 수 있다. 상술한 방법으로 인접하는 18개의 기지국 각각의 최적 수신전력(

)을 구할 수 있다. 또한 특정 기지국 내에 이동단말기의 수를 하나씩 증가하면서 구한 최적의 수신 전력을 구한 후 [수학식 3]의 조건을 만족하는지를 검토하여 해당 기지국의 최대 용량을 산출할 수 있다.Solving Equation 3 using linear programming (LP), we have 19 ({P} `_ {1} ^ {*}, {P}` _ {2} ^ {*}, ... {P} `_ {19} ^ {*}). Of the 19 powers determined, the optimal power of cell i is

Is determined. That is, if one equation (3) is solved by linear programming, 19 receive powers can be obtained, of which the first receive power is the optimum receive power of the cell. However, since the system capacity of a particular base station is determined by the reception power of the base station and the power that interferes with the neighboring base station, it is necessary to determine the reception power of the neighboring base station as well as the reception power of the corresponding base station to minimize the amount of interference from the neighboring base station. There is. Therefore, the following procedure is used to find the optimal reception power of 18 adjacent cells. That is, if one of the 18 neighboring base stations is designated as the center cell, the equation (3) is redefined by considering the traffic of the center cell and 18 neighboring cells with respect to the cell, and solved according to the linear programming method. The power value of can be found. With the above-described method, the optimal reception power of each of 18 adjacent base stations

) Can be obtained. In addition, after obtaining the optimal reception power obtained by increasing the number of mobile terminals within a specific base station, the maximum capacity of the base station can be calculated by examining whether the condition of Equation 3 is satisfied.

[Table 1] below shows the number of mobile terminals in a call in each cell.

When the number of mobile terminals as shown in [Table 1] is accommodated in each of sixty cells having a hexagonal cell model, the optimal reception power of each base station is obtained by the linear programming method as shown in Table 2 below.

The maximum number of mobile terminals that can be accommodated using the optimal power obtained in [Table 2] is shown in [Table 3] below.

When using the optimal reception power obtained by linear programming from the specific base station and 18 neighboring base stations from Table 3, it can accommodate about 20% more mobile terminals than when all the base stations are allocated to the same reception power. You can see that.

1 is a flow chart for determining the reception power of a base station that has requested a call and 18 neighboring base stations when a new call request is received from a new mobile terminal according to the present invention. When a new call request is made to a specific base station, the control station determines the optimal base station reception power based on the linear programming method of Equation (3).

As shown in FIG. 1, when a mobile terminal in a base station requests a new call (1), it notifies the control station managing the base station (2). The control station notified of the new call request (1) determines the 19 optimal reception powers based on the linear programming method of Equation 3 using the base station as the central cell (3). The first optimal reception power is selected from the determined 19 optimal reception powers to be the optimal reception power of the base station (4). After determining whether or not it is the last base station among the 18 neighbor base stations (5), if it is not the last base station, one of the base stations is selected (6).

The selected arbitrary base station is determined as the center cell, and the optimal reception power of 19 base stations is determined using the linear programming method of Equation 3 (7). The first optimal reception power is selected from the 19 optimal reception powers to determine the optimal reception power of the corresponding center cell (8).

The above-described process is applied to all 18 neighboring base stations to find the optimal reception power of the base station and the 18 neighboring base stations that make the initial call request. A power control, that is, a closed circuit power control, is performed to keep the power of the mobile station reaching the base station the same based on the optimal received power (9).

As described above, when the optimal reception power obtained by the linear base method is calculated using the power received by a specific base station and 18 adjacent base stations, it is possible to accommodate about 20% more mobile terminals than when all the base stations are allocated to the same reception power. It has an effect.

Claims (1)

The control station notified of the new call request determines the optimal reception power of the cell based on the linear programming method of Equation 3 using the base station as the central cell; Selecting one base station in sequence among a plurality of neighboring base stations and obtaining an optimal reception power of the base stations by the linear programming method of Equation 3 around the corresponding cell; And performing power control to maintain the same power of the mobile terminal reaching the base station on the basis of the optimal reception power of the base stations obtained as described above. [Equation 3] minimization

Conditional Expression

0P_l <= 1,

Where N _i is the number of mobile terminals in the i cell, W is the spread bandwidth, R is the transmission rate, P _i is the reception power of the base station i, η ₀ is the background noise, and f _ij is the i cell by the mobile terminal in the j cell. Represents the ratio of interference to and I_l and J_l are exponents representing the number of cells in the first and second stages surrounding celll.

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